Most of the available solar energy collectors for residential use are of "flat plate" construction. Parabolic or other types of concentrating collectors are becoming more practical and economically attractive, as they are capable of operation at higher temperature ranges.
The temperature within the collector panel is maintained at reasonable levels by heat transfer out of the panel to the fluid being pumped through the collector grid or piping circuits.
Failure of the pumping unit or a power failure will result in loss of flow, and the fluid temperature in the conduits (as well as the inside of the panel) can reach destructive levels.
Backup systems are not economically feasible since they require a reserve power source such as batteries, and hence cannot be considered dependable unless the electrical charge of the batteries is checked regularly.
Considering that power failures can result in extremely high temperatures inside of the panel, and the resultant possibility that severe component damage can occur, protective safety devices must be used.
With inexpensive non-metallic internal materials of construction, it is not economically practical or safe to rely solely on fireproofing treatment because of possible loss of effectiveness at elevated temperatures over extended periods of time.
According to present teaching and practice, most collectors are subjected to "stagnation" tests to determine a safe temperature operating range. In most instances the highest predictable temperature is the design criteria that dictates the selection of materials.
Material selection based on highest expected temperature plus a reasonable safety factor often results in an unnecessary requirement for materials that are relatively expensive and of considerable weight. Low density materials of construction generally have low thermal expansion characteristics and they tend to have lower ignition temperatures than do high density materials such as metals.
With the ambient temperature outside the panel always being well below the ignition temperature of the materials of construction, this invention describes the use of a device for opening a port in the side of the collector so that the hot air can escape. A preferred form of the automatic opener is a fusible plastic membrane which will soften, rupture, or liquify when reaching a predetermined temperature, thereby allowing outside air at ambient temperature to enter through apertures that are normally sealed off by the separator. When the separator ruptures or melts, heated air will escape and cooler ambient air will purge the inner cavity of the panel, thus maintaining internal temperatures below the ignition temperature of low density members.
Other safety systems may be used, but in the event that they fail, the inexpensive and replaceable nature of the device of the present invention makes it practical to use this device as the only protective means against damage from excessive heat.